Fluid mixing is a key operation for a variety of processes. For example, fluid mixing is an important unit operation for lab-on-a-chip (LOC) bio-analysis system where often quick and efficient mixing of reactants is required. In the case of a microfluidic mixer, the mixer has to provide a sufficiently mixed solution in a confined length of the micro-device, such as before the point where detection is taking place.
Fluidic devices made by MicroElectroMechanicSystem (MEMS) technology are generally termed microfluidics, which have channel dimensions ranging from microns to a few millimeters. Since it is possible to perform micro fabrication with high accuracy and low cost due to the development of lithography-based processing, microfluidic devices such as mixing apparatus (micro mixer), chemical reactors (micro reactor), micro TAS (Total Analysis System: LOC) and microchemistry plants are all known.
Mixing in microfluidic devices can be provided by active mixing systems or passive mixing systems. Active mixing systems utilize one or more powered sources to enhance mixing, such as vibrational sources to induce vibration in the microchannel. The need to supply power and its associated powered source adds to the cost, complexity and usefulness in certain mixing applications.
Passive systems provide a versatile solution to simplify the design and fabrication of microfluidic devices, and are highly compatible with current microfabrication techniques. Hence, passive mixing systems provide a cost-effective mixing solution. In a conventional T-mixer or Y-mixer, 2 microchannels having a small channel width (e.g., 50-100 μm) are merged into a single microchannel (e.g. 100 μm channel width) in which mixing takes place. Due to the small dimensions of the microchannels, fluid flow is generally highly laminar and mass transport in the mixing channel occurs only by diffusion, normal to the flow direction. To improve mixing, passive mixing systems can include shaping of the mixing microchannel (e.g., a serpentine or wavy constant width microchannel), or flow obstacles within the mixing microchannel.